Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
1119 am CDT Sat Mar 15 2014
Aviation/18z tafs/...frontogenetical band will affect portions of
SC WI this afternoon and Erly this evening. Not yet getting any
ground truth with this. At this point thinking of leaving precipitation
out of tafs altogether based on trends. Favorable Delta T sets up
this evening with 850 temperatures into the negative teens celsius.
Clouds/flurries cannot be ruled out. Big decrease in low level relative humidity
after 6z...so any precipitation will be prior to then...be it from the
band or any lake effect precipitation. Not a big deal either way. Any
lake clouds may lower to MVFR levels otherwise expecting mainly
VFR conditions into Sunday with clear skies becoming dominate later
tonight and for Sunday with high pressure gaining full control.
Previous discussion... /issued 422 am CDT Sat Mar 15 2014/
Today and tonight...forecast confidence medium
Stratus clouds over central WI are moving more southward as the boundary
layer flow veers north. Thus some broken cloud cover is likely over
southeast WI this morning. A few flurries are possible over east central
WI. Otherwise middle level clouds will increase later this morning as
850-700 mb frontogenesis spreads into southern WI and northern Illinois. The
frontogenesis is due to a confluent zone between the polar vortex
over Ontario Canada and the upper trough moving across the Central
Plains. Models have some differences on how far north the snow will
initially set up over the County Warning Area before sliding southward as cold and dry air
advection develop on brisk northeasterly winds.
Went with likely probability of precipitation west and south of Madison with only 20-30 probability of precipitation
north and east of Madison this afternoon and early evening. The northeasterly
winds and lake to 850 mb temperature differences around 13c will contribute
to a lake effect potential tonight from Milwaukee southward but believe it
will stay very light due the arrival of dry air. The snow accumulate
forecast is 1/2 to 1 inch for the counties bordering Illinois including
Iowa County as well. The cold advection and decreasing clouds will
drop temperatures into the single digits to middle teens by 12z sun.
A cold airmass under high pressure is expected for Sunday. Winds
will be breezy between the center of the high will be just to the
north and low pressure passing by well to the south. The winds and
surface to 850 mb temperatures are favorable for lake effect snow...especially
Sunday morning...but it looks like too much subsidence and dry air
from the high pressure. May struggle to even See Lake effect clouds.
Monday through Wednesday...forecast confidence...medium
Models continue to waffle with light snow chances Monday and Monday
night. Overall...looks like pretty decent warm air aloft with middle
level saturation...but very dry conditions below 700 mb. Will keep
the forecast dry for now.
Strong low pressure is expected to move through the region Tuesday
and Wednesday. Models are in better agreement now with the track of
the surface low...generally taking it over or north of the forecast
area. This will spell mainly rain for southern Wisconsin...possibly
mixing with or changing to a little snow Tuesday night into
Wednesday as colder air wraps in behind the low.
Thursday and Friday...forecast confidence...medium
Kept the forecast dry for Thursday as high pressure slides by to the
south. Have some low probability of precipitation Friday...as models bring another low
through the area. With the low tracking right at the forecast area
.Looks like rain again given current model solutions.
Aviation/12z tafs/...stratus clouds over central WI are moving more
southward as the 1000-850 mb winds veer north. Thus southeast WI taf sites could
see a period of broken cloud cover around 3.5-4.0 kft this morning.
Cannot completely rule this out for kmsn but lower chances there.
Otherwise middle level clouds will increase this am from Iowa and Minnesota with
light snow to follow mainly south of Madison and Milwaukee due to
850-700 mb frontogenesis. Do expect at least very light intermittent
snow at kmsn and kenw this afternoon. The snow may the linger into
the evening over far southeast WI due to lake effect snow but this to will
be very light. Ceilings may fall briefly to 2.0-3.0 kft during the
snowfall at kmsn and kenw along with visibilities of 2-3 miles.
Marine...a Small Craft Advisory is in effect tonight into Sunday
afternoon south of Port Washington. Brisk northeast winds will
develop tonight and continue into Sunday as the pressure gradient
tightens between low pressure over the lower Mississippi River
valley and polar high pressure moving into the northern Great Lakes.
High waves will develop since most of the ice has melted. The winds
and waves will subside by late Sunday afternoon.
Lm...Small Craft Advisory from 10 PM this evening to 4 PM CDT Sunday
Today/tonight and aviation/marine...gehring
Sunday through Friday...ddv